Originally Posted by
contango
The very basic description from my user manual is that it creates tiny bubbles that appear and implode, lifting the dirt off the item. How it works, how the bubbles appear, and why their implosion lifts the dirt off the item are the bits I don't understand.
Sounds like some more time on Google is required.
Search "cavitation" and you'll get more info.
Basically, since water can't stretch, pulling it apart creates spaces. You might have seen this happens when running a speedboat propeller too fast. Sound is a compression wave, alternatingly squeezing and pulling the medium (water) apart, so as high energy sound passes through water, small cavities are created then immediately collapsed.
This action doesn't actually do anything in terms of cleaning by itself. It's just mechanical action like the agitator in a washing machine, but it's the cleaning solvent that actually does the cleaning. Imagine the difference between dipping something in a lake to clean it, and holding it under the surf at the beach.